The lymphatic vasculature has been implicated in a variety of pathophysiological processes, including tumor metastasis, tissue inflammation, edema, impaired immune surveillance and disrupted fat absorption. Nevertheless, it is remarkable that modern medicine has yet to discover pharmacologically-tractable targets for the modulation of lymphatic vessel growth or function; largely because the molecular mechanisms that control lymphangiogenesis remain poorly understood. Our lab has shown that adrenomedullin (AM), a 52-amino acid peptide that is secreted by lymphatic endothelial cells (LECs), is essential for proper embryonic lymphatic vascular development and that fine-tuned control of AM dosage is critical for the regulation of both embryonic and pathological lymphangiogenesis. CXCR7 was originally identified as an AM receptor, but has more recently been studied for its functions as a decoy receptor for SDF-1. Our preliminary studies suggest that CXCR7 is expressed in developing LECs and that CXCR7-/- mice exhibit lymphatic phenotypes consistent with AM overexpression. Therefore, I propose to investigate the hypothesis that CXCR7 serves as a decoy receptor for AM which consequently provides fine-tuned control of AM-mediated proliferation of LECs. I will perform comprehensive phenotypic analysis of lymphangiogenesis in loss-of-function CXCR7-/- mice in order to define the role of CXCR7 during in vivo lymphangiogenesis. In addition, I propose to cross CXCR7-/- mice to mice that are haploinsufficient for AM in order test whether the decoy activity of CXCR7 is required for the control of AM- mediated lymphangiogenesis in vivo. I will also use both loss-of-function and gain-of-function in vitro models to elucidate whether CXCR7 dampens AM-mediated downstream signaling. LECs will be cultured and treated with AM for proliferation assays, immunoblot, and 3D spheroid sprouting assays to explore the role of CXCR7 on AM-mediated LEC proliferation, downstream signaling, and mature vessel formation. Results from this proposal will define the role of CXCR7 in AM signaling and lymphangiogenesis and may elucidate novel therapeutic targets for the treatment of poorly managed lymphatic vascular diseases.